Determination of the opening size of granular filters

Abstract

AbstractGranular filters are used in hydraulic earthen structures as a natural barrier to protect base soils from erosion under seepage conditions. Their performance is greatly dependent on the pore space connectivity that provides transport pathways for migrating fine particles. Traditional filter design rules are based on characteristic particle diameters of the involved materials, which do not explicitly reflect the pore structure dimensions. Even though the literature offers some mathematical tools that can be used to characterize the opening size of granular filters, the underlying physical fundamentals are still not sufficiently understood. Therefore, this study aims to provide a plausible physical framework for determining the filter opening size by means of numerical simulations using the discrete element method. From the investigation of particle transport processes in polydisperse packings of spheres, the opening sizes associated to these numerical filters are defined on the basis of their constriction size distribution. A mathematical procedure is then introduced to determine the effective opening size of the filter and subsequently, a revised retention criterion for granular filters is proposed and validated with experimental data from the literature. The study findings can offer a valuable perspective for erosion assessment methods in both new and existing earthen structures.